No. 2.] EARLY DEVELOPMENT OF AMBLYSTOMA. 373 



mesoblast. When the blastopore has narrowed to a slit, the 

 chorda {ch.) consists of a single layer of hypoblast but few 

 cells in width, as shown in Fig. 9. 



Reconstructions show an irregular outline, the enlargements 

 and constrictions often appearing in such order that they sug- 

 gest the possibility of a metameric arrangement. The later 

 development is essentially the same as observed in other Am- 

 phibia. The layer of columnar hypoblast folds up, and is 

 gradually constricted until it lies free in the mid-dorsal region. 



3. Experiments. 



Before considering the embryonic area, I wish to record the 

 results of certain experiments. 



The experiments were made on the eggs of Amblystoma 

 tigrinum during March and April, 1893, in the Morphological 

 Laboratory of the University of Michigan. 



A method was sought by which I might be able to distinctly 

 mark the surface of the egg and at the same time interfere as 

 little as possible with normal development. After a number 

 of methods were tried the following one was adopted : The 

 outer envelopes are removed from the Qgg, which is then 

 placed in a watch crystal on a bed of cotton, with barely enough 

 water to cover it. The egg is then rotated until the desired 

 point is uppermost, when it is punctured with an extremely 

 fine hair held by forceps. A small quantity of the protoplasm 

 oozes out and forms a minute extra-ovate, which remains at- 

 tached to the Qgg. The eggs thus marked are transferred to 

 watch crystals, in which they remain until the embryo is 

 formed. A large mirror is fastened to the stage of a dissect- 

 ing microscope ; on this the watch crystals are arranged in 

 series, and the eggs examined by means of an extension arm. 

 The image of the opposite side may be thus observed during 

 the entire period, from the time of marking until the embryo 

 is formed. This is necessary, since the very small extra-ovates 

 are easily detached. 



Since to record these experiments in detail would require 

 considerable space, I confine myself to a brief summary. 



